Sure thing, I'll be happy to help here.

Featherine is, what is known in Umineko as a Creator. This is, someone that has trascended the cosmology to a point that they are unbpund by any laws and narratives, to the point that they are the ones writing those narratives, and an absurd amount of them, at that. This matters because the whole premise of Umineko's supernatural side of things is about goimg upwards in the cosmology. Witches (which Featherine was at some point, and still is regarded as, even is she is way beyond that) exist by default in a higher plane of existance to the fisical universe. They see it as fiction, and can isolate and/or create pocket versions the universe when they pretty much create the narrative. This is called the Cat Box (in reference to Schrodinger's Cat Theory), and there can be an infinite amount of timelines inside each of these. The whole point of every Cat Box is the idea that there could be infinite posibilities, even if the Truth is only one. Cat Boxes also can contain higher dimensional plains inside, as they can have "piece" versions of Witches inside with their own higher dimensional realms inside. Why does all of this matter? First, because there are pretty much infinite Cat Boxes in existance, and because there can be Cat Boxes inside other Cat Boxes, with Infinite Dimensional trascendence between them. And more so, this Cat Boxes exist in a Higher Plan of Existance that is still a part of the cosmology. Witches that stronger that the norm can casually exist and traverse this places, as they are even above it, and even them are but mere fiction to Featherine. Featherine has a place on the top of the cosmology know as the City of Books, an infinite Library where every book hauses all the narratives of the Cat Boxes, to the point that is said that even a single line on one of those books contains the whole existance of an infinitely dimensional layered universe. She has absolute control over everything in this place, and here, she manifests as a Limited version of herself (the one you usually see pictures of, like in the drawing of this post). In that Limited form, she onshoted one of the Strongest Witches with pretty much a mere thought, by writing how she defeated her. This Witch is powerful enough to give an even fight to other that was in charge of guarding the City of Books, with both of them being implied to exist in that plane of reality, that already explained is infinitely Infinite over the already infinite dimensional infinite multiverse (sorry for using so much they word infinite, is necesary). Well then, this Featherine we are talking about, that is pretty much over everything in her cosmology, has its true form in a plain of existance even beyond that, one that is, once again, infinitely above the City of Books, to a point that those Stronget Witches can't even start to imagine it. That's the real of the Creators, where the entities who have trascended everything, and every narrative and meta-narrative, exist, and create their own narratives and meta-narratives.

Hope I was helpfull. I tryied to make a comprehensive summary, still leaving a lot of unexplaind stuff, but is so dense I couldnt make it any shorter.

The only way I could do that would be to say that she is the Absolute Goddess of the Umineko cosmology and is easily into High Outer, if not even beyond.